1. Field of the Invention
The present invention pertains to seismic acquisition, and, more particularly, to a method of collecting data during a seismic acquisition.
2. Description of the Related Art
Seismic surveying traditionally involves imparting acoustic waves from an acoustic source that propagate through subterranean geological formations and are reflected back to seismic sensors. The seismic sensors are deployed in arrays and are positioned through the area being surveyed. The reflected signals are transformed into electrical or optical signals that are then transmitted over electrical or optical cables to a data collection unit. In a land-based survey, the data collection unit is usually housed on a recording truck. The data collection unit either records the signals it receives, analyzes them in real-time, transmits them to a remote location for analysis, or some combination of these things.
Recent trends in seismic surveying are producing larger arrays of seismic sensors. These arrays are larger both in terms of coverage area and in terms of the number of seismic sensors. The larger arrays adversely impact the cost of conducting the survey. Not only do these larger arrays employ more pieces of equipment, but their extended coverage area lengthen deployment time. The more time it takes to deploy the array, and the more pieces of equipment it uses, the more expensive the survey.
Attempts in the art to address these factors include U.S. Pat. No. 6,226,601, entitled “Seismic Survey System,” and issued May 1, 2001, to Trimble Navigation Limited as assignee of the inventor Harold L. Longaker (“the '601 patent”). In particular, this patent discloses a wireless seismic system in an effort to eliminate, or at least minimize, cabling. The system includes multiple layers of “cells.” The seismic sensors are grouped in a particular fashion, and each group of seismic sensors wirelessly transmits its data to a dedicated, first level transceiver. The first level transceivers are similarly grouped, and each group of first level transceivers wirelessly transmits the data accumulated from its group of seismic sensors to a dedicated, second level transceiver. This process repeats, and each higher level sees a further consolidation of data from the previous layer. At some point, the data is completely consolidated or has reached some desired level of consolidation. The consolidated data is then wirelessly transmitted to a data collection unit.
Conventional wireless approaches, such as the one in the '601 patent mentioned above, use a variety of communications protocols. These communications protocols include:                GSM-DCS, or Global System for Mobile Communications-Digital Cellular System, which employs a form of time-division multiplexing called Time Division Multiple Access “TDMA”), used for cellular telephony in much of Europe and Asia;        UMTS, or Universal Mobile Telecommunications System, used to deliver broadband information at speeds up to 2 Mbit s/sec, including audio and video, to wireless devices anywhere in the world through fixed, wireless and satellite systems;        DECT, or Digitally Enhance Cordless Telecommunications, a common standard for cordless personal telephony originally established by the European Telecommunications Standards Institute (‘ETSI’), a European standardization body, for cordless business communications;        CDMA, or Code-Division Multiple Access, a digital cellular technology that uses spread-spectrum techniques; and        GPRS, or General Packet Radio Service, a standard for wireless communications which runs at speeds up to 115 kilobits per second and supports a wide range of bandwidths.However, the application of each of these protocols brings its own problems. For instance:        UMTS, DECT, and CDMA are telephony oriented, rather than network oriented, which imposes undesirable restrictions on communication of data in a seismic acquisition environment;        UMTS is unproven in terms of its components;        UMTS and GSM have the same upstream bandwidth as downstream bandwidth, which is wasteful in a seismic acquisition system needing a much higher upstream bandwidth than downstream bandwidth;        GPRS allocates more than one channel downstream and sometimes none upstream, which is contrary to the needs of a seismic acquisition system;        GSM-DSC causes a poor use of the number of channels in the cell versus the possible range of the cell because of a disparity between the density of geophones in the cell and the surface area of the cell; and        GSM-DSC still employs a wire between its base transceiver unit (“BTS”) and the Basic Station Controller (“BSC”) and between the BSC and the central recording and processing system.Thus, current wireless techniques applied in seismic acquisition leave much to be desire.        
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.